1. Field of the Invention
This invention relates generally to a magnetic head for a disk drive, and more particularly to a magnetic write head having a pole piece with a double pedestal structure.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) or giant magnetoresistive (GMR) read head to form a merged head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces terminate at the ABS where they define first and second pole tips, respectively. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces magnetic write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS fringe across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to and a short distance (fly height) from the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR or GMR read head.
An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers, and located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head, the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic flux from the circular tracks of the rotating disk by a change in resistance that corresponds to the strength of the fields. A sense current is conducted through the MR sensor, where changes in resistance cause voltage changes that are received by the processing circuitry as readback signals.
A GMR read head includes a GMR sensor which manifests the GMR effect. In the GMR sensor, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron, cobalt, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. A GMR head is typically associated with a design in which the second shield layer and first pole piece are not a common layer. These pieces are separated by a non-magnetic material, such as alumina, or a metal that can be deposited using a physical vapor deposition technique or an electro-plating technique, for example.
One or more heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged head is mounted on a slider that is carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates, an air layer (an “air bearing”) is generated between the rotating disk and an air bearing surface (ABS) of the slider. A force of the air bearing against the air bearing surface is opposed by an opposite loading force of the suspension, causing the magnetic head to be suspended a slight distance (flying height) from the surface of the disk. Flying heights are typically less than 0.02 μm in today's disk drives.
Prior art described in U.S. Pat. No. 5,864,450 entitled “Ni45Fe55 Metal-In-Gap Thin Film Magnetic Head” teaches the utilization of an additional material on top of the pole tip which has a higher saturation magnetization than that of the material beneath it. This advantageously improves the write performance of the write head. However, this technique is limited in application to a write head which requires higher magnetic moment materials sputtered on top of the pole tip with a throat height being more or less aligned with the bottom pole tip. Prior art described in published U.S. patent application Ser. No. 20020191334 entitled “Magnetic Transducer With Pedestal Pole Piece Structure” teaches a writer structure having a sunken first layer coil to achieve a shorter yoke length for writer efficiency and a substantial planar surface to facilitate a top pole process having enhanced pole width control. As the throat height, typically about 2 μm, is defined by the bottom P1 pedestal, this structure suffers from mechanic reliability problems when the pedestal length is smaller than 0.5 μm, or the aspect ratio (pedestal height/pedestal length) is greater than 2.5. Thus, this prior art is not extendible to relatively short write throat applications.
Write heads must continuously be improved to provide better overwrite (OW) capabilities and reduced fringing fields as track pitch increases with reduced write track width and write gap. In FIG. 9, a graph 900 shows a three-dimensional finite-element calculation of deep gap field vs. the current-coil-turn product (where N is coil turns and I is current through the coil). As apparent from graph 900, a short throat height is imperative to achieve a high deep gap field for narrow track write heads, which corresponds to a higher write field for superior writeability.
What is needed is an improved write head design and apparatus which provides for a reduced throat height and a superior mechanical stability.